Less is more with Apple Computer’s very tiny and very hot new iPod shuffle digital music player. But it’s also less.

Introduced last week at the big Macworld show in San Francisco by Apple boss Steve Jobs, the shuffle will be perfect for some people, some of the time. But the shuffle can’t deliver the exact songs you want on demand, unlike true iPods, putting Apple at risk of disappointing confused shuffle buyers who expect more.

The shuffle is certainly a wonder to behold. Smaller than a pack of gum, as Apple illustrates on its Web page for the shuffle (www.apple.com/ipodshuffle), the white plastic player weighs an airy three-quarters of an ounce. The headphones you use to listen to the Shuffle may be heavier and take up more space.

Also, the shuffle’s two models are very affordable. The model with 512 megabytes of storage, enough for eight hours of music, is only $99; the model with 1 gigabyte, enough for 16 hours, is only $149. That’s less than other digital music players with equivalent capacity, although I expect the shuffle’s arrival to cause some quick markdowns from competitors.

You may have trouble, by the way, getting a shuffle right now. Apple put a limited number of units on sale last week at its company-owned store in San Francisco in what may have been more a publicity event than a product launch. As of late last week, Apple’s online store said the 512MB model would be available in two to three weeks, and the 1GB model in three to four weeks. It could be even longer before the shuffle shows up in the many retail stores that now sell the iPod.

To understand how the shuffle can be so small requires a brief technology backgrounder, so please stick with me.

The original iPod, including the recently added iPod mini and iPod photo, store digital music on a hard disk drive. The good thing about hard disks is huge capacity; the top-of-the-line 60-gigabyte iPod holds a staggering 1,000 hours of music – enough to listen non-stop for six weeks. The bad thing about hard disks is that they’re relatively big and prone to skip when jostled.

The shuffle instead uses “flash,” or rewritable, memory chips. The good things about flash are that it’s light, durable and will never skip. The bad thing about flash is that it’s considerably more expensive than hard disks per gigabyte, so flash players have much less storage.

The challenge with flash players is cramming a display screen and controls into ever-smaller packages. Apple cut through the dilemma by eliminating the display screen, allowing the shuffle to be smaller and offer more battery life – 12 hours – than other flash players, but making it nearly impossible to select the music tracks you want to hear.

Full iPods do have a display screen, allowing you to scroll through your music collection by song, artist or album. You also can assemble multiple personal playlists on your computer – such as collections specifically for parties or exercising – and select among them. You can’t do any of this with the shuffle.

What inspired the shuffle, Jobs said last week at Macworld, is the popularity of the “shuffle” feature on full iPods, which randomly selects music from your entire library. When you’re in the mood to be surprised by songs you forgot you owned, shuffle is perfect.

This is what the shuffle does best, no surprise.

The shuffle comes with a white-string lanyard for hanging the player around your neck, white earbud-style headphones and a CD for installing the necessary software. You’ll need a Windows computer running either Windows XP or Windows 2000, or a Macintosh computer running OS X to connect.

You take the cap off the bottom of the shuffle, revealing a USB plug. You stick the gum-pack-like player into a computer to load up the shuffle with music using Apple’s excellent and free iTunes software. There’s even a clever “Autofill” feature that will grab tracks from your library at random. You unplug the shuffle when loaded, then hit the play button to hear your songs in no particular order.

The shuffle’s battery recharges through the USB port, in about four hours. An optional $29 adapter, due in a few weeks, allows you to recharge the shuffle away from your computer. You also can use the shuffle as a “thumb drive” for storing data files.

The simple shuffle controls do only three things: play/pause, volume up/down, and track forward/back. Pressing and holding the play button for three seconds locks the controls, preventing accidental button-pressing when the shuffle is riding around in a pocket or purse.

The shuffle also has a “playlist” mode, where it runs through the songs in the order you loaded them. If you’ve just purchased a new album, for instance, you can put those 10 or 12 tracks at the top of your playlist and be sure to hear them by using playlist mode.

But there’s no realistic way to find a song in the middle of a fully loaded 512MB Shuffle with 120 songs or a 1GB Shuffle with 240 songs. If you know you want to hear song number 87, you could hit fast-forward 86 times, supposing you could remember the title of song 87. You also can’t look at the shuffle to see the name of a song you don’t recognize.

I own a 15-gigabyte hard-disk iPod that I’ve loaded with 9 gigabytes of my favorite music, roughly 200 albums. There are moments when I just have to hear Little Feat’s “Dixie Chicken,” and the iPod can oblige. The shuffle can’t.

Not that I dislike the shuffle. I spent several days testing the 512MB model last week and came away impressed. The sound quality is outstanding, as good as my hard-disk iPod. The shuffle works seamlessly with iTunes, so anyone familiar with the iPod will face no learning curve.

If you want to listen in shuffle mode, or run through a single playlist from beginning to end, the shuffle does the job. Especially for listening while moving around – exercising at the gym, running, snowboarding or cycling – the shuffle is a much better choice than the more delicate hard-disk iPods.

The biggest problem for Apple will be educating buyers to understand what the shuffle does and doesn’t do. If I were in charge of iPod marketing, I’d be especially concerned that first-time buyers who get a shuffle won’t fully appreciate the magic of iPod, because they’ll miss the joy of getting the music they want at the exact moment they want to hear it.